Portable wireless communication devices typically experience a wide range of operating environments. The differing environments include differing physical environments as well as differing electronic environments, which may be related to the physical environments, but may be independent of the physical environment.
Physical environments include location, topography, weather conditions, as well as a host of other environmental conditions. Electronic environments include spectrum loading, the presence or absence of intentional or unintentional jamming signals, channel conditions, as well as other electronic environmental factors. The physical and electronic environments can combine in ways that widely affect the signal quality received by a portable wireless communication device.
The signal power received at a receiver can vary over a tremendous range. A receiver that is located in close proximity to a transmitter may receive a substantial signal, while a receiver that is located a large distance from the transmitter may receive a very weak signal. Path loss attributable to distance from a transmitter can itself be sufficient to degrade the signal quality at a receiver. Other physical and electronic environments can combine with distance to further extend the range of signal power over which the receiver is expected to operate. It is not uncommon for a portable receiver to experience an 80 dB dynamic range of incident power.
A receiver can include an Automatic Gain Control (AGC) loop, circuit, or module in order to at least partially compensate for the range of signal power incident on the receiver. The AGC module attempts to maintain a substantially constant signal power at a predetermined signal processing location within the receiver. The AGC module typically amplifies the received signal using a variable gain amplifier.
The AGC module compares a characteristic of the amplified signal, such as the amplified signal power, the amplified signal amplitude, or the amplified signal magnitude, at the predetermined signal processing location against a predetermined threshold value, referred to as the AGC setpoint, AGC threshold, or simply the setpoint. If the amplified signal characteristic is less than the AGC setpoint value, the AGC module increases the gain of the variable gain module. The AGC module is able to increase the gain of the variable gain amplifier up to a predetermined maximum gain. If the amplified signal characteristic is greater than the AGC setpoint, the AGC module decreases the gain of the variable gain module. The AGC module is able to decrease the gain of the variable gain amplifier down to a predetermined minimum.
The difference between the predetermined maximum and the predetermined minimum represents the AGC range. The AGC module can operate to maintain a substantially constant signal power at the predetermined signal processing location over the entire AGC range.
However, if the received signal includes substantial interfering signal sources, the AGC module may control the gain based on the composite signal having the desired received signal and received interfering signals.